1. Field of Invention
This invention relates generally to omnidirectional isotropic antennas, and more particularly, to omnidirectional antennas that transceive isotropic radiation patterns using a dielectric lens structure.
2. Discussion
Omnidirectional isotropic antennas are extremely important in transmitting and receiving electromagnetic radiation patterns where the direction is variable and it is undesirable to use pointing or detecting mechanisms. Known omnidirectional isotropic antennas are capable of producing uniform patterns in azimuth but not routinely in elevation. That is, the pattern is azimuthally symmetric but is not isotropic. Antennas that produce isotropic radiation patterns can be used with transponders, walky-talkies, automobile radios and cellular telephones. For these applications the antenna must be relatively small to be portable. In addition, at millimeter wave frequencies these antennas can be difficult and expensive to manufacture.
Certain known antenna structures capable of producing isotropic radiation are physically quite large. For example, there is disclosed in U.S. Pat. No. 5,283,590, granted to Gary G. Wong, a procedure for modifying the RF pattern electronically which results in a rather large antenna structure. Antennas that are required to transceive millimeter electromagnetic waves in the range of 38 Ghz to 95 Ghz and higher, are of necessity quite small in size. Other prior patents teaching omnidirectional performance such as U.S. Pat. No. 5,450,093, granted to Chang S. Kim, employ a waveguide encircled with helical dielectric strands. Such an antenna may be useful for radiation in the microwave frequency range, but at millimeter wave frequencies, a very small structure would be required which would be difficult to fabricate. The helical antennas also require a phasing circuit which electronically provides the necessary circular polarization. The instant invention provides in combination with its dielectric lens insert polarization structures, passband filters, and an impedance matching element that are integral with the dielectric lens.